Among solid image pickup devices, a CCD (Charge Coupled Device) image pickup device has a high sensitivity and a small amount of white blemishes. However, when the CCD image pickup device is at a high temperature or captures an image with high sensitivity and accumulates it, the CCD image pickup device has a large amount of white blemishes.
Thus, the related art has little pixel defect (the so-called white blemish) with a very high dark current. However, the dark current approximately doubles depending on an increase in the temperature of the CCD image pickup device at 6° C. Also, the dark current increases in proportion to an electron multiplication and accumulation time. Thus, the dark current increases when the CCD image pickup device is at a high temperature or captures an image with high sensitivity and accumulates it. Namely, white blemish appears.
In order to reduce the influence of white blemish at an optical black pixel part, respective vertical pixel signals of an output of 12 lines at a vertical-optical black (V-OB) part of the CCD image pickup device are averaged and stored as a signal of one line portion, and the stored signal is subtracted from an output signal of an effective pixel part of the solid image pickup device (see Japanese Patent Application Publication No. 1995-067038).
Also, a solid image pickup apparatus using a CCD image pickup device is promoted to have a reduced vertical smear so that the CCD image pickup device cannot be affected by a dark current or a high level compression caused by the defective pixel such as white blemish generated in the CCD image pickup device.
Thus, the following (1) or (2) may be performed.
(1) An average signal of respective vertical pixels (V-OB) signals of four lines of a vertical light block image is calculated, their horizontal signals are averaged, a low level and a high level are compressed, and it is subtracted from an image signal outputted from effective pixels of a light receiving face of the CCD image pickup device (see Japanese Patent Application Publication No. 2007-150770).
(2) A dark current unevenness in a vertical direction of a screen of four lines of the vertical light block pixel (V-OB) signal is corrected. Next, a second value from a minimum value of the respective vertical pixel signals of the 4 lines of the vertical light block image V-OB is calculated and stored as a vertical smear correction signal, and it is subtracted from an image signal after performing AGC (Automatic Gain Control) on the effective pixels of the light receiving face of the CCD image pickup device. Also, a signal outputted from the solid image pickup device is converted from analog to digital having 14 bits, the representative value signal is calculated and attenuated into 15/16, and it is subtracted from an image signal outputted from the effective pixels of the light receiving face of the CCD image pickup device (see Japanese Patent Application Publication 2008-109639).
Further, with an increase in the integration degree of a digital signal processing circuit, the storing and the arithmetic process of output signals of a plurality of lines can be easily realized not only in a memory integrated DSP (Digital Signal Processor) dedicated for use of a video image but also in a reasonable general-purpose FPGA (Field Programmable Gate Array). However, it is required to reduce a gradation (bit number) in a signal processing to suppress the increase in the volume of circuit.
Further, an FEP (Front End Processor) has been spread. The FEP includes therein a CDS (Correlated Double Sampling) for removing noises from a signal outputted from the CCD image pickup device, a variable gain amplification (automatic gain control: AGC) unit for correcting a dark current and adjusting gain, and an ADC (Analog-to-Digital Converter) for converting the signal into a digital video signal Vi. Although a gradation of the ADC of the FEP has conventionally been equal to 10 bits, a gradation of 12 or 14 bits is generally used and a processor having a gradation of 16 bits has also been realized as a product. The FEP in which the gradation of the ADC is set to 22 bits and an AGC unit is arranged behind the ADC has also been realized as a product. Low band noise is noticeable when the FEP in which the ADC has the gradation of 12 bits is combined with a ⅔ type CCD image pickup device for NTSC (National Television System Committee) having a wide dynamic range.
On the other hand, low band noise is not noticeable when the FEP in which the ADC has the gradation of 14 bits is combined with an output signal of the ⅔ type CCD image pickup device for NTSC having the wide dynamic range. However, even in the FEP in which the ADC has the gradation of 14 bits, some low band noise is noticeable at 74 MHz having small timing margin when the PEP is combined with a ⅔ type CCD image pickup device for HDTV (High Definition Television), for example, although 36 among 55 number of H-OB (Horizontal-Optical Black) are clamped. Moreover, a DNRIC (Digital Noise Reduction Integrated Circuit) system having a frame memory therein has come into the market.
The hand-trembling electronic correction is performed by reading out a video signal stored in an image memory from a position that is moved horizontally and vertically by the hand-trembling and combining the video signal and a movement detecting signal such that the identical points of an original target are overlapped.
In an OFDM (Orthogonal Frequency Division Multiplexing) image transfer including guard band which repeats a part of an effective signal, FPGA is used and a received OFDM signal is complex-multiplied with the OFDM signal delayed for a period of effective symbol and is added to the result. Further, the absolute value of I component and the absolute value of Q component of guard correlation are added, and a level of the received signal is computed from a square value of a peak value or from the mean value of a square root value of the square value (refer to Japanese Patent Application Publication No. 2003-115787).
Further, in the OFDM transfer, a received OFDM signal is complex-multiplied with the OFDM signal delayed for a period of effective symbol and is added to the result, and thereby carries out a correlation operation. Thereafter, a peak position of the absolute value of a correlation signal obtained by the correlation operation is detected, the absolute value of I component and the absolute value of Q component of the correlation signal at the detected peak position is calculated and added, a peak value is calculated, and a level of the received signal is calculated from a addition-and-average value of either square value of the peak value or a square root value of the square value (refer to Japanese Patent Application Registration No. 4107824).
Also, an electron multiplying CCD (EM-CCD) can have increased sensitivity by being combined with an electron cooling unit, so such can monitor quasi-video for nighttime image capturing of visible light and near infrared light.
The EM-CCD can increase sensitivity by being combined with electron cooling. For example, when an amplitude voltage of electron multiplying electrode (hereinafter, referred to as a ‘CMG’) of the EM-CCD is increased 0.1V, the amplification rate is increased 1.4 times, and when the temperature of the EM-CCD is lowered 11° C., electron multiplication factor is increased 1.8 times. Thus, a voltage amplitude of a driving waveform is required to be secured, a high stability is required, and heating is required to be reduced. Namely, power consumption needs to be reduced.
Also, the electron multiplication factor is highly correlated to the amplitude voltage of the CMG, and is generated with the probability of 0 to 2% per CMG one end. For example, when the electron multiplication factor is 1% per one end, 640 ends of the CMG of the EM-CCD has an electron multiplication factor of 583 times as 649 multiplication of “1.01”. Therefore, when the amplitude voltage of the CMG is increased 0.1V, the electron multiplication factor of the EM-CCD is increased 1.4 times. Thus, the electron multiplication factor is irregularly fluctuated at a very low frequency, and image signals are irregularly modulated, generating aliasing. Also, when a multiplication sensitivity of a low incident light amount level side of the electron multiplication is increased, noise on an image of the screen is conspicuous even to the naked eyes, and the effective sensitivity is drastically degraded. Further, in case of high electron multiplication, the electron multiplication factor is degraded because of accumulation of the product of the high electron multiplication factor and the incident light amount. Thus, the amplitude of the CMG voltage must be necessarily minimized by electron-cooling the EM-CCD more intensively (see Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3). However, the EM-CCD needs to be used in a hermetically closed state, a heat generation unit must be electron-cooled, and an image pickup apparatus itself is accommodated in a hermetically closed space, and air is convection-circulated with a cooling fan. Thus, heat releasing is difficult and the cooling effect of the electron cooling is small.
However, in an image pickup apparatus such as a television camera using the EM-CCD, there may occurs a case where a cooling unit included in the EM-CCD is not able to cool or heat anymore due to an influence of the surrounding temperature. In this case, to keep a constant sensitivity of the EM-CCD, a method has been disclosed that detects a temperature of EM-CCD and controls the electron multiplication factor based on the detected temperature (see Japanese Patent Application Publication No. 2007-318735).    [Non-Patent Document 1] T I TC246RGB-B0680x 500 PIXEL IMPACTRON™ PRIMARY COLOR CCD IMAGE SENSOR SOCS087—DECEMBER 2004—REVISED MARCH 2005    [Non-Patent Document 2] Hamamatsu Photonics Principle and Technology of High Sensitivity Cameras Cat No. SCAS0020J01 DECEMBER 2006 (summary of electron multiplication factor)    [Non-Patent Document 3] ANDOR Technical Note Longevity in EMCCD and ICCD Part I-EMCCD 14 Mar. 2006 (measures for preventing deterioration of electron multiplication factor as time elapses)
In the abovementioned technologies, the electron multiplication factor is degraded by an accumulation of the product between the electron multiplication factor and the quantity of incident light, as time elapses. Therefore, not only the effective sensitivity is further degraded but also detection of dark current proportional to electron multiplication factor is difficult.
Further, as described above, an amplification factor increases 1.4 times when an amplitude voltage of CMG of EM-CCD rises by 0.1 V, the electron multiplication factor increases 1.8 times when a temperature of EM-CCD lowers by 11° C. For this reason, it is required for the image pickup apparatus using EM-CCD to guarantee a voltage amplitude of driving waveforms and high stability and to suppress heat generation (i.e., to reduce power consumption). Also, since dark current is also electron-multiplied, unevenness of dark current on the screen are seen like opaque glass, and in the event of the high electron multiplication, the electron multiplication factor is degraded by an accumulation of the product between the electron multiplication factor and the quantity of incident light. Thus, it is difficult to correct the unevenness of dark current.
In addition, since the electron multiplication occurs stochastically, the electron multiplication irregularly changes at a very low frequency, aliasing that unevenness of dark current and an image signal are irregularly modulated at a very low frequency takes, place to become a prominent interdigital type noise, degrading a signal-to-noise (S/N) ratio and drastically lowering the effective sensitivity.
However, it is difficult to precisely correct an irregular 1/f fluctuation.